1. Technical Field of the Invention
The present invention relates to coated hard alloy blade members or cutting tools having exceptional steel and cast iron cutting ability for both continuous and interrupted cutting.
2. Background Art
Until now, the use of a coated cemented carbide cutting tool made by using either chemical vapor deposition or physical vapor deposition to apply a coating layer of an average thickness of 0.5-20 .mu.m comprised of either multiple layers or a single layer of one or more of titanium carbide, titanium nitride, titanium carbonitride, titanium oxycarbide, titanium oxycarbonitride, and aluminum oxide (hereafter indicated by TiC, TiN, TiCN, TiCO, TiCNO, and Al.sub.2 O.sub.3) onto a WC-based cemented carbide substrate for cutting steel or cast iron has been widely recognized.
The most important technological advance that led to the wide usage of the above-mentioned coated cemented carbide cutting tool was, as described in Japanese Patent Application No. 52-46347 and Japanese Patent Application No. 51-27171, the development of an exceptionally tough substrate wherein the surface layer of a WC-based cemented carbide substrate included a lot of Co, a binder metal, in comparison with the interior, whereby the fracture resistance of the coated cemented carbide cutting tool rapidly improved.
In addition, as disclosed in Japanese Patent Application No. 52-156303 and Japanese Patent Application No. 54-83745, the confirmation that, by sintering the WC-based cemented carbide containing nitrogen in a denitrifying atmosphere such as a vacuum, the surface layer of the WC-based cemented carbide substrate can be made from WC-Co which does not include a hard dispersed phase having a B-1 type crystal structure, whereby it is possible to cheaply produce WC-based cemented carbide having more Co in its surface layer than in the interior, was also important.
Concerning the advancement of the coating layer, coated cemented carbides having coating layers wherein the X-ray diffraction peaks of the Ti compounds such as TiC, TiN, and TiCN have a strong (200) orientation and the Al.sub.2 O.sub.3 has an .alpha.-type crystal structure such as described in Japanese Patent Application No. 61-231416 and coated cemented carbides having coating layers wherein the X-ray diffraction peaks of the Ti compounds such as TiC, TiN, and TiCN have a strong (220) orientation and the Al.sub.2 O.sub.3 has a .kappa.-type crystal structure such as described in Japanese Patent Application No. 62-29263 have little variation in the tool life.
Furthermore, Japanese Patent Application No. 2-156663 shows that a coated cemented carbide having a coating layer wherein the TiC has a strong (111) orientation and the Al.sub.2 O.sub.3 is of the .kappa.-type has the features that there is less spalling of the coating layer and has a long life.
However, since the Ti compounds such as TiC of Japanese Patent Application No. 61-231416, Japanese Patent Application No. 62-29263, and Japanese Patent Application No. 2-156663 are coated by the normal CVD method, the crystal structure is in a granular form identical to the coating layers of the past, and the cutting ability was not always satisfactory.
Additionally, Japanese Patent Application No. 50-16171 discloses that coating is possible with the use of organic gas for a portion of the reaction gas, at a relatively low temperature. In this patent, the crystal structure of the coating layer is not described, and furthermore, the crystal structure may have a granular form, or the crystals may grow in one direction (elongated crystals) depending on the coating conditions. Moreover, in the references given in this patent, the coating layer is made up of only TiCN, and Al.sub.2 O.sub.3 is not disclosed. Additionally, this TiCN had a low bonding strength with the substrate.